Combining NodeJS-based passport auth and ReactJS frontend

if you are using Passport then, you just need to read the strategy docs. I am assuming the authentication is done through Oauth

Example with express

Routes.js

api.route('/auth/github')
    .get(PassportCtrl.auth);

  api.route('/auth/github/callback')
    .get(PassportCtrl.authCallback, PassportCtrl.redirect);

PassportCtrl.js

import passport from 'passport';

const auth = passport.authenticate('github', {
  scope : ['profile', 'email']
});

const authCallback = passport.authenticate('github');

const redirect = (req, res) => {
    res.redirect('/whereveryouwant');
}

const getAuthUser = (req, res) => {
  res.json({
    user : req.user
  })
}

const logOut = (req, res) => {
  req.logOut();

  res.redirect('/');
}

export default {
  auth,
  authCallback,
  redirect,
  getAuthUser,
  logOut
}

passport init

// adding cookie feature
app.use(cookieSession({
  maxAge : 30 * 24 * 60 * 60 * 100,
  keys : [process.env.COOKIE_SECRET]
}));

// initializing passport
app.use(passport.initialize());
app.use(passport.session());

I forgot, you have to proxy

webpack.config.js

 devServer: {
    proxy: { // proxy URLs to backend development server
      '/auth/github': 'http://localhost:3001',
      '/api/**' : {
        'target' : 'http://localhost:3001'
      }
    },
    hot : true,
    contentBase: path.join(__dirname, "dist"),
    historyApiFallback : true,
    compress: true,
    port: 8080
  }

React

import React from 'react';
import {connect} from 'react-redux';
import {Link} from 'react-router-dom';


class Header extends React.Component {
  renderContent () {
    const {auth} = this.props;
    switch (auth) {
      case null : return;
      case false : return (
        <li><a href='/auth/google'>Login with google</a></li>
      )
      default: return ([
        <li key={'logout'}><a href='/api/logout'>Log out</a></li>
      ])
    }
  }
  render () {
    const {auth} = this.props;
    return (
      <nav>
        <div className='nav-wrapper'>
          <Link className="left brand-logo" to={auth ? '/whereveryouwant' : '/'}>
            Your page Name
          </Link>
          <ul className='right'>
            {this.renderContent()}
          </ul>
        </div>
      </nav>
    );
  }
}

const mapStateToProps = (state) => {
  return {
    auth : state.auth
  }
}

export default connect(mapStateToProps)(Header);